Rotaviruses comprise a genus within the family Reoviridae, and are ubiquitous throughout the animal kingdom. Rotavirus infection is known to cause gastrointestinal disease and is considered the most common cause of gastroenteritis in infants. In fact, essentially every species of domestic animal tested has its own endogenous rotaviruses that cause diarrhea in newborns. Rotaviruses are also thought to be the most significant cause of gastroenteritis in young children and animals. Kapikian & Chanock, Rotaviruses, Virology, 2nd edition, Fields et al, eds., New York: Ravenpress, 1353-1404 (1990). Rotaviruses cause diarrheal disease primarily in the young, but infection and disease in older children and adults are also common.
Rotavirus infection is the leading cause of human diarrhea both in developed and developing countries, especially in infants less than one year of age. Worldwide approximately 870,000 children die of rotavirus associated disease every year in developing countries. Even in the United States there are approximately 70 deaths and 200,000 hospitalizations per year due to rotavirus diarrhea. While mortality has been controlled in developed countries by universal access to emergency medical care, morbidity from rotavirus disease remains high.
Around 90% of infants and children develop a rotavirus infection by the third year of life whether they are living in a developed or developing country. The impact of the disease is substantial. An estimated 3,000,000 cases of rotavirus diarrhea occur in the United States annually, leading to some 500,000 physician visits and 55,000-100,000 hospitalizations, which costs the health care system an estimated $500,000,000 to $600,000,000 a year. When indirect costs are included, the figure rises to $1.4 billion. Pediatrics, 609-615 (1995).
Rotaviruses are double-stranded RNA viruses and contain a multi-segmented genome. Because the viral genome is arranged in segments, these viruses are capable of genetic reassortment. This reassortment occurs when two or more rotaviruses infect a single cell and the various viral segments reassort during the packaging of new virus particles assembled in the cytoplasm of infected cells. The ability of the virus to reassort its genome components results in a great diversity of immune responses generated against the virus. This ability has also made generation of a rotavirus vaccine extremely challenging.
A variety of different approaches have been taken to generate a rotavirus vaccine suitable to protect human populations from the various serotypes of rotavirus. These approaches include various Jennerian approaches, use of live attenuated viruses, use of virus-like particles, nucleic acid vaccines and viral sub-units as immunogens.
An example of a Jennerian vaccine can be found in Zygraich, U.S. Pat. No. 4,341,763, issued Jul. 27, 1982, entitled, “Methods of Vaccinating Humans Against Rotavirus Infection.” In this reference, bovine rotaviruses, either attenuated or inactivated, were used to immunize human beings against rotavirus infection. A modified Jennerian approach has also been adopted with the goal of attaining broader antigenic coverage. This approach entailed engineering new reassortant rotavirus types so that a group of viruses would simultaneously display epitopes of various serotypes. However, as with all attenuated viruses, there is always a high risk of reversion.
The Food and Drug Administration has recently approved a multivalent vaccine against rotavirus making it available to pediatricians in the United States. The vaccine, which was developed by Albert Z. Kapikian, M D, and colleagues at the Laboratory of Infectious Diseases (NIAID) is an excellent example of a multivalent vaccine. A recent reported study conducted in Caracas testing this vaccine was reported in the New England Journal of Medicine 1997; 337, 1181-1187. Among some 2,200 infants enrolled in the double-blind, placebo controlled study, the vaccine was successful in reducing severe diarrheal illness in about 70% of subjects but was less effective at reducing the incidence of less serious diarrheal illness. Recently, it was reported that there have been serious side effects such as bowel blockage associated with this vaccine.
Another example of the modified Jennerian approach is found in Clark et al., U.S. Pat. No. 5,626,851, issued May 6, 1997, entitled, “Rotavirus Reassortant Vaccine.” In this example a rotavirus reassortant suitable for use as a vaccine was produced using genetic reassortment between an attenuated bovine rotavirus and at least one rotavirus representing an epidemiologically important serotype. This reference looked to create a bovine rotavirus that carried either VP4 or VP7 genes which, when presented to a immunologically naive subject, would induce a protective immune response therein. Thus, this method relies upon the use of whole viruses to immunize a subject.
U.S. Pat. Nos. 4,624,850, 4,636,385, 4,704,275, 4,751,080, 4,927,628, 5,474,773, and 5,695,767, each describe a variety of rotavirus vaccines and/or methods of preparing the same. A commonality shared by the members of this group is that each of these vaccines relies on the use of whole viral particles to create the ultimate rotavirus vaccines. Given the long standing need for an effective, multivalent vaccine, it is clear that this body of work has been only partially successful in addressing the need for such a vaccine.
Departing from traditional methods of vaccine generation, advances in the field of molecular biology have permitted the expression of individual rotavirus proteins. Using these techniques, vaccine candidates generated from virus-like particles of different protein compositions have shown potential as subunit vaccines. In one reference, VLPs containing VPs 2 and 6 or VPs 2, 6, and 7 were administered to mice with and without the addition of cholera toxin. O'Neal et al., “Rotavirus Virus-like Particles Administered Mucosally Induce Protective Immunity,” J. Virology, 71(11):8707-8717 (1997). Both types of VLPs induced protective immunity in immunized mice, although protection was more effective when the VLPs were administered with cholera toxin (CT). In a subsequent study by the same group, the Escherichia coli heat-labile toxin (LT) was compared to CT for effectiveness in producing rotavirus protection. O'Neal et al., “Rotavirus 2/6 Virus-like Particles Administered Intranasally with Cholera Toxin, Escherichia coli Heat-Labile Toxin (LT), and LT-R192G Induce Protection from Rotavirus Challenge,” J. Virology, 72(4):3390-3393 (1998). This group concluded that both the wild-type LT and a recombinant form of the molecule were effective adjuvants when immunizing with rotavirus VLPs.
Core-like particles and VLPs have also been used to immunize cows. Fernandez, et al., “Passive Immunity to Bovine Rotavirus in Newborn Calves Fed Colostrum Supplements From Cows Immunized with Recombinant SA11 rotavirus core-like particle (CLP) or virus-like particle (VLP) vaccines,” Vaccine, 16(5):507-516 (1998). In this study the ability of CLPs and VLPs to create passive immunity was studied. This group concluded that VLPs were more effective than CLPs in inducing passive immunity.
In several studies the individual viral proteins have also been used to immunize subjects. For example, one group used bacculovirus-expressed VP4 protein from the simian rhesus rotavirus (RRV) to parenterally immunize murine dams. Newborn mice suckling from immunized dams were found to be protected against RRV challenge and against challenge by a murine rotavirus through a passive immunity scheme. Mackow et al., “Immunization with bacculovirus-Expressed VP4 Protein Passively Protects Against Simian and Murine Rotavirus Challenge,” J. Virol. 64(4): 1698-1703 (1990).
Rotavirus proteins have even been used as immunological carrier complexes to facilitate the presentation of other epitopes to a subject. In one reference, VP6 was chosen as a carrier molecule for a particular antigen, based on the viral protein's ability to bind peptides. Sabara, et al., U.S. Pat. No. 5,374,426, issued Dec. 20, 1994, entitled, “Rotavirus Nucleocapsid Protein VP6 in Vaccine Compositions.”
Exploiting another avenue, research has also been performed where a protective immune response was elicited using a DNA vaccine. Herrmann, et al., U.S. Pat. No. 5,620,896, issued Apr. 15, 1997, entitled, “DNA Vaccines Against Rotavirus Infections.” While the results from this method are interesting, the degree of protection found in mice immunized with plasmids containing either the VP4, VP7 or VP6 genes in a murine retrovirus were very limited. Moreover, there are at least two reports of rotavirus DNA vaccines that failed to provide any protection to the immunized animal from rotaviral infection. Choi, et al., “Particle Bombardment-Mediated DNA Vaccination with Rotavirus VP6 Induces High Levels of Serum Rotavirus IgG but Fails to Protect Mice Against Challenge,” Virology 232: 129-138 (1997). Choi et al. “Particle Bombardment-Mediated DNA Vaccination With Rotavirus VP4 or VP7 Induces High Levels of Serum IgG but Fails to Protect Mice Against Challenge,” Virology 250:230-240 (1998).
This review of the state of the art attempts to provide some measure of the extent of time and energy that has been expended to date to develop an effective rotavirus vaccine. Yet, even with the most successful efforts to date, even the severe forms of rotaviral disease can be prevented only bout 75% of the time. Given this limitation, there remains a need for a safe and effective rotavirus vaccine, which overcomes the above deficiencies. The vaccine of present invention is designed to remedy and eliminate these problems.